Update Handoff workflow to match current APIs (#741)

Author: jeffhandley

agent-framework/user-guide/workflows/orchestrations/handoff.md

@@ -81,9 +81,9 @@ Define which agents can hand off to which other agents:
 ```csharp
 // 3) Build handoff workflow with routing rules
 var workflow = AgentWorkflowBuilder.StartHandoffWith(triageAgent)
-    .WithHandoff(triageAgent, [mathTutor, historyTutor])  // Triage can route to either specialist
-    .WithHandoff(mathTutor, triageAgent)                 // Math tutor can return to triage
-    .WithHandoff(historyTutor, triageAgent)              // History tutor can return to triage
+    .WithHandoffs(triageAgent, [mathTutor, historyTutor]) // Triage can route to either specialist
+    .WithHandoff(mathTutor, triageAgent)                  // Math tutor can return to triage
+    .WithHandoff(historyTutor, triageAgent)               // History tutor can return to triage
     .Build();
 ```
 
@@ -143,8 +143,8 @@ math_tutor: I'd be happy to help with calculus integration! Integration is the r
 ## Key Concepts
 
 - **Dynamic Routing**: Agents can decide which agent should handle the next interaction based on context
-- **AgentWorkflowBuilder.StartHandoffWith()**: Defines the initial agent that starts the workflow
-- **WithHandoff()**: Configures handoff rules between specific agents
+- **AgentWorkflowBuilder.CreateHandoffBuilderWith()**: Defines the initial agent that starts the workflow
+- **WithHandoff()** and **WithHandoffs()**: Configures handoff rules between specific agents
 - **Context Preservation**: Full conversation history is maintained across all handoffs
 - **Multi-turn Support**: Supports ongoing conversations with seamless agent switching
 - **Specialized Expertise**: Each agent focuses on their domain while collaborating through handoffs